SAMPLE ANSWER 2E Using the formula for velocity, making sure all values are in their standard unit:
v s t 80
20 4. The body has a velocity of 4 m s1 west.
It is often necessary to convert units from those given in the question to their SI unit.The conversion between kilometres per hour and metres per second is shown below.
SAMPLE PROBLEM 2F
Convert: (i) 120 km h1 to metres per second
(ii) 5 m s1 to kilometres per hour
SAMPLE ANSWER 2F
v s t 120 1 000
120 km h1
60 60 120 000 3 331/3 m s1.
: : 3 3
(i)120 km h1 is the same as (120 1000) m per (60 60) s Using the formula for velocity:
3 600 100 3 331 3 .
(ii) The conversion from km h1 to m s1 can be done by dividing by 3.6. 5 m s1 is the same as 5 (60 60) metres per hour 5 m s1 18 000 m h1 18 km h1 The conversion from m s1 to km h1 can be done by multiplying by 3.6.
DISPLACEMENT s a
u v 2 b
t
u initial velocity v final velocity s displacement t time
Displacement in terms of average velocity For numeric calculations, displacement is defined as the product of ‘average velocity’ and ‘time travelling’.
displacement average velocity time travelling
* a SAMPLE PROBLEM 2G
What is the displacement of a body as it changes velocity from 2 m s1 east to 10 m s1 east over a period of 5 s?
